To prepare a 0.1 M solution of hydrochloric acid (HCl) from a concentrated 37% solution, we will need to carry out a few calculations. Here are the steps to follow:
Step 1: Find the Molarity of the Stock Solution
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Determine the density of the stock solution: Given as 1.19 g/cm³.
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Concentration of HCl in 37% solution: This means 37 g of HCl are present in 100 g of the solution.
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Calculate the mass of the solution in 1 liter (1000 g): \[ \text{Mass of solution} = \frac{1000 , \text{g solution}}{100 , \text{g}} = 1000 \times 0.37 , \text{g HCl} = 370 , \text{g HCl} \text{ in 1000 g of solution} \]
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Find the number of moles of HCl in 370 g:
- Molar mass of HCl ≈ 36.46 g/mol \[ \text{Moles of HCl} = \frac{370 , \text{g}}{36.46 , \text{g/mol}} \approx 10.14 , \text{mol} \]
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Calculate the molarity of the stock solution: \[ \text{Molarity (M)} = \frac{\text{Moles}}{\text{Volume in L}} = \frac{10.14 , \text{mol}}{1 , \text{L}} \approx 10.14 , \text{M} \]
Step 2: Calculate the Volume of Stock Solution Needed
Now that we have the molarity of the stock solution, we can calculate how much we need to dilute to get 0.1 M in a 100 mL solution.
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Use dilutions formula: \( C_1V_1 = C_2V_2 \)
- Where:
- \( C_1 \) = concentration of stock solution (10.14 M)
- \( V_1 \) = volume of stock solution needed (in L)
- \( C_2 \) = concentration of the diluted solution (0.1 M)
- \( V_2 \) = final volume of diluted solution (0.1 L)
Plug in the known values: \[ (10.14 , \text{M}) \times V_1 = (0.1 , \text{M}) \times (0.1 , \text{L}) \] \[ 10.14 , V_1 = 0.01 \] \[ V_1 = \frac{0.01}{10.14} \approx 0.000985 , \text{L} \approx 0.985 , \text{mL} \]
- Where:
Step 3: Prepare the Solution
To prepare the desired concentration of HCl:
- Measure approximately 0.985 mL of the concentrated HCl solution using a pipette.
- Dilute with distilled water in a 100 mL volumetric flask. Add distilled water until the total volume reaches the 100 mL mark.
Step 4: Safety Measures
- Always wear appropriate personal protective equipment (PPE) such as gloves, goggles, and a lab coat when handling concentrated acids.
- Perform all dilutions in a fume hood or well-ventilated area to avoid inhalation of fumes.
Summary
To prepare a 0.1 M HCl solution in 100 mL, you need to take approximately 0.985 mL of 37% HCl and dilute it with distilled water to a final volume of 100 mL.